Aerodynamic Design Of An Ultra-Highly Loaded Booster Of A High Bypass Ratio Turbofan

Based on an existing high bypass ratio turbofan,this paper uses a new concept of diffusion blade profiles with large camber and low flow losses to design a rotor for the booster which characterizes the low wheel speed,thus achieving ultra-high loading of the rotor,effectively increasing its stage pressure ratio and reducing the weight of the booster.Utilizing mature blade design and optimization platform,a two-dimensional(2D)design method of S1(blade to blade)/S2(hub to tip)stream surfaces is applied to design the blades of the rotor and the stator in the booster,and the 2D blade profiles in the S1 stream surface are designed by means of an optimization design method.The flow fields in the original and newly designed boosters are simulated by using a numerical method.This thesis is divided into two parts.One part is about the aerodynamic design of an ultra-highly loaded booster with only one stage,which is designed to replace the original booster with three stages.The main aerodynamic parameters of the original booster are used as the design target of the new one-stage booster.The original booster was moderately loaded,and its total pressure ratio is 1.298 due to the low wheel speed.Additionally,as a result of the low stage pressure ratio,the flow losses in the stators have a large influence on the efficiency of the booster;therefore,its efficiency is quite low(0.807).To achieve the equivalent total pressure ratio of the original booster(1.298),the rotor total pressure ratio at the design point of 1.33 was selected in consideration of the flow losses in the matching stator for the newly designed booster with only one stage.According to the results of the S2 through-flow calculation,the diffusion factor first rises and then declines with an increase in the total pressure ratio(or load coefficient).The diffusion factors at the rotor hub and tip are approximately 0.35 and 0.6,respectively,when the rotor total pressure ratio is 1.33.The result indicates that aerodynamic design of the rotor and its matching stator are feasible.And the ultra-highly loaded booster rotor was obtained by the S1 flow profile optimization design and the radial product stacking.The NUMECA software was used to calculate teh flow fields in the rotor,and it can be seen that the total pressure ratio and isentropic efficiency at the design point are 1.33 and0.9702,respectively.Meanwhile,the surge margin is 16.5%.What’s more,it can be seen that there are two advantages to using this highly cambered blade profile.On one hand,it can increase the twisted velocity,and the specific work,as a result,the total pressure ratio of a rotor increases.On the other hand,the convergent flow path in rear section of the cascade contributes to controlling thedevelopment of the boundary layer on the blade suction surface,thereby reducing the flow losses and improving the rotor efficiency.The 2D design method of S1/S2 stream surfaces is further applied to design the blades of the stator.The designed rotor,the matching stator,as well as the original IGV constituted a new booster.Furthermore,the effects of the rise of the hub on the aerodynamic performance of the booster were studied,and the results indicate that the lift angle of 5 degree of the hub can contribute to controlling the development of the boundary layer on the blade suction surface,thereby reducing the flow losses.By calculating the flow fields in the new booster,the total pressure ratio(1.293)is near the design objective(1.298),while the isentropic efficiency and the surge margin are higher than the objective.To exam the matching performance of the newly designed booster with the original S-shaped intermediate case,the flow fields of the booster plus the intermediate case are also calculated.As a result,the total pressure ratio and the isentropic efficiency of the booster both decrease after matching the intermediate case,which are 1.267 and 0.7849,respectively.The flow losses in the intermediate case mainly come from the local diffusing in the case bottom.The other part is about the aerodynamic design of a two stage booster,which is aimed at replacing the original booster with three stages and achieving higher total pressure ratio and isentropic efficiency.The rotors and stators in the two stage booster were designed by using the same method as the one stage one.The only difference between them is that the blades in the two stage booster were also optimized by using the 3D optimization method.To make sure that the spanwise distribution of total pressure at the outlet of the booster is even,the total pressure of the first-stage rotor is distributed linearly and the rotor was obtained by the optimization design method.In addition,a new concept of blade profiles with large camber is used to design the first-stage matching stator.The outlet tangential flow angle of this stator is opposite to the rotation direction of the rotor,which was set as 33 degree.It must be mentioned that there are two advantages to using this highly cambered stator blade profile.On one hand,the convergent flow path in rear section of the cascade contributes to controlling the development of the boundary layer on the blade suction surface,thereby reducing the flow losses.On the other hand,the negative prespin can be used effectively.Furthermore,the aerodynamic performance of the stator was improved by using the 3D optimization design method and lifting the hub.As a result,the total pressure ratio and isentropic efficiency of the first stage at the design point are 1.33 and 0.9702,respectively.Due to the lack of time,the aerodynamic design of the second-stage rotor and stator haven’t been completed.